1. Field of the Invention
The present invention relates to a method for setting a dental glass ionomer cement that is used for restoring a tooth in the dental remedy or the like.
2. Description of the Conventional Art
Variety of dental cements is generally used in the remedy of teeth. Representative examples include a zinc phosphate cement in which zinc oxide is reacted with phosphoric acid, a carboxylate cement in which zinc oxide is reacted with a polycarboxylic acid, a resin cement using the polymerization of an acrylic monomer, a calcium hydroxide cement in which calcium hydroxide is reacted with an oily component, a zinc oxide eugenol cement in which zinc oxide is reacted with eugenol, and a glass ionomer cement using a fluoroaluminosilicate glass powder and a polycarboxylic acid.
These dental cements are widely used in the dental remedy. More specifically, they are widely used for cementing a dental prosthesis such as a crown, an inlay, and a bridge, or cementing an orthodontic device and a dentin, for filling a tooth cavity, for sealing pit and fissure in enamel, for lining, and for rebuilding base and core.
Of these, the dental glass ionomer cement has a superior biocompatibility, it has adhesive properties to a tooth structure and a set cement thereof is translucent and superior in esthetics, and it has an advantage in that it gradually releases after setting fluorine with a lapse of time, thereby a caries resistant function can be expected. Accordingly, the dental glass ionomer cement is a dental cement that is most generally used in the wide variety of applications in the dentistry.
This dental glass ionomer cement is a dental cement in which a a fluoroaluminosilicate glass powder and a polycarboxylic acid as the major components cause a setting reaction in the presence of water and are set. More specifically, an aqueous polyacrylic acid solution exerts the fluoroaluminosilicate glass powder to liberate metal ions (such as alkali metal ions, alkaline earth metal ions, and aluminum ion) in the glass, which then undergo ionic bonding to a carboxyl group of the polyacrylic acid, to form a crosslinking structure, thereby causing gelation and setting (this reaction will be hereinafter sometimes referred to as "ionomer reaction"). And, it is also known that the dental ionomer cement continues to cause the ionomer reaction after the initial setting, so that the compressive strength of a set cement thereof gradually increases for one year after the start of the setting.
In addition, there is developed a resin reinforcement type of a dental glass ionomer cement in which a dental glass ionomer cement is compounded with a polymerizable monomer, thereby utilizing a polymerization reaction with the monomer in combination with the ionomer reaction. This resin reinforcement type of a dental glass ionomer cement is improved in terms of mechanical strengths such as bending strength and adhesive properties to a tooth structure, as compared with the conventional dental glass ionomer cement that causes the setting only relying upon the ionomer reaction.
The method for setting the dental glass ionomer cement is generally carried out in the following manner. That is, the fluoroaluminosilicate glass powder and the aqueous polyacrylic acid solution are respectively weighed and mixed in an appropriate ratio on a mixing pad for exclusive use by means of an instrument such as a spatula; or prescribed amounts of the fluoroaluminosilicate glass powder and the aqueous polyacrylic acid solution are respectively weighed and accommodated in a capsule so that the fluoroaluminosilicate glass powder and the aqueous polyacrylic acid solution are isolated from each other, and at the time of use, the partition is broken to mix fluoroaluminosilicate glass powder and the aqueous polyacrylic acid solution with each other by means of a capsule mixer or the like. The resulting mixture is filled in or applied on a cavity or pit and fissure in enamel. Some products which is also available include a hydraulic dental ionomer in which a mixture of a fluoroaluminosilicate glass powder and a polyacrylic acid powder is provided to undergo setting upon mixing with water. Therefore, the glass ionomer cements according to the present invention comprise the fluoroaluminosilicate glass powder, the polycarboxylic acid and water for setting.
As described above, since the dental glass ionomer cement uses the ionomer reaction, a time is required for the initial setting. Thus, it is impossible to perform the next clinical operation until the initial setting. Further, it is pointed out that the dental glass ionomer cement has a defect called as sensitization to water: that is, before or after the initial setting, when a surface of the dental glass ionomer cement mixture comes into contact with water, metal ions elute during the setting reaction, or the content of water increases, whereby the cement surface becomes cloudy or brittle, ultimately leading to a decrease of the surface performance after the setting. This is caused due to the ionomer reaction of the dental glass ionomer cement which is an acid/base reaction between the fluoroaluminosilicate glass (base) and the polycarboxylic acid (acid radical) in the presence of water and is sensitively influenced by water from outside.
In order to overcome this defect, the following measure was carried out. That is, the dental glass ionomer cement before the initial setting is filled and applied carefully so that it does not come into contact with water from outside such as saliva and then a moistureproof material called as a varnish such as resin-based materials is applied and dried to form a coating film on the dental glass ionomer cement surface, so as to effect a moistureproofing for 20 to 25 minutes during the initial setting.